1. Field of the Invention
The present invention is related to the use of electromagnetic interference (EMI) shields in electronic devices, and more particularly to the use of EMI shields in mobile stations.
2. Description of Related Art.
Electromagnetic interference (EMI) shields are used to attenuate the EMI generated, and otherwise received, by various electronic devices including mobile stations. Generally, shielding materials are capable of reflecting, absorbing or preventing radio frequency signals from either entering or exiting an enclosed area that is surrounded by the shielding material.
Originally, shielding consisted of a sheet of conductive metal material that was effective in shielding against a broad band of electromagnetic radiation. However, as electronic devices became more complex they became more susceptible or likely to generate specific radio frequency signals at higher power levels. For metal shields, effectively shielding such specific frequencies and power levels would require a very thick shield that is prohibitively heavy and bulky for most mobile stations.
More recent versions of EMI shields include a sheet of conductive material and an additional absorptive member combined with the conductive member. The absorptive member attenuates surface currents on the conductive member and absorbs, reflects, breaks up or redirects electromagnetic radiation. Typically, the material properties required to have such effects on electromagnetic radiation include conductivity, dielectric constant and magnetic permeability that are tailored as known to those skilled in the art to attenuate signals having a particular frequency. An absorptive member can generally be formulated with the right materials and structure to provide a high level of shielding within the frequency ranges most susceptible to interference.
For instance, absorptive members may be constructed of a block of silicone, urethane, or other material having absorptive properties that is attached to the conductive member using a pressure sensitive or absorptive adhesive. Alternatively, multiple conductive and absorptive coatings may be applied directly to the conductive member. Attachment of the absorptive member using adhesive or the application of coatings occurs after the conductive member has been soldered to a circuit board of the mobile station so as to avoid the adverse effects of soldering process temperatures.
Despite the advantages provided by shields combining metal conductive members with absorptive materials, adhesive attachment of the absorptive member is prone to failure. In addition, the application of coatings requires repeated coatings and cure time to reach a thickness sufficient to satisfy shielding requirements.
Therefore, it would be advantageous to have an EMI shield including a conductive member and an absorptive member that is easily manufactured. In particular, it would be advantageous if the EMI shield could be constructed without the use of adhesives or multiple applications of coatings.